Security has been stepped up at Norwich Castle Museum after a number of items celebrating the life of the Norfolk naval hero Lord Nelson were taken.
The news comes at a time the museum's displaying an Italian masterpiece worth £100 million.
Police are reviewing CCTV and the National Security Adviser for the Arts Council is reviewing the museum's security arrangements.
The theft was noticed by an off-duty police officer who saw the cabinet which housed the objects had been tampered with.
More top news
Anglia Weather: Frosty start with sunshine later
Becoming clear and frosty overnight. Bright and dry on Monday.
An Essex councillor is appealing for help to find out what happened to her "beautiful, much-adored" daughter after she was found dead.